#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 510;
int n,m;
int g[N][N];
int dist[N];
bool st[N];

int dijkstra(){
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    for(int i = 0; i < n; i ++)
    {
        int t = -1;
        for(int j = 1; j <= n; j ++)
        {
            if(!st[j] && (t == -1 || dist[t] > dist[j]))
                t= j;
        }

        for( int j = 1; j <= n ; j ++)
        {
            dist[j] = min(dist[j], dist[t] + g[t][j]);

        }
        st[t] = true;

    }
    if(dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}

int main(){
    scanf("%d%d", &n, &m);
    memset(g, 0x3f, sizeof g);
    int a, b, c;
    while(m--){
        scanf("%d%d%d", &a, &b, &c);
        g[a][b] = min(g[a][b], c);

    }
    cout << dijkstra();
    return 0;
}